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A brain tumor or intracranial neoplasm occurs when abnormal cells form within the brain. There are two main types of tumors: malignant or cancerous tumors and benign tumors.〔 Cancerous tumors can be divided into primary tumors that start within the brain, and secondary tumors that have spread from somewhere else, known as brain metastasis tumors.〔 This article deals mainly with tumors that start within the brain. All types of brain tumors may produce symptoms that vary depending on the part of the brain involved.〔 These may include headaches, seizures, problem with vision, vomiting, and mental changes. The headache is classically worst in the morning and goes away with vomiting.〔 More specific problems may include difficulty in walking, speaking and with sensation.〔〔 As the disease progresses unconsciousness may occur.〔 The cause of most brain tumors is unknown.〔 Risk factors that may occasionally be involved include a number of inherited conditions known as neurofibromatosis as well as exposure to the industrial chemical vinyl chloride, the Epstein-Barr virus, and ionizing radiation.〔〔〔 While concern has been raised about mobile phone use, the evidence is not clear.〔 The most common types of primary tumors in adults are: meningiomas (usually benign), and astrocytomas such as glioblastomas.〔 In children, the most common type is a malignant medulloblastoma.〔 Diagnosis is usually by medical examination along with computed tomography or magnetic resonance imaging.〔 This is then often confirmed by a biopsy.〔 Based on the findings, the tumors are divided into different grades of severity.〔 Treatment may include some combination of surgery, radiation therapy and chemotherapy.〔 Anticonvulsant medication may be needed if seizures occur.〔 Dexamethasone and furosemide may be used to decrease swelling around the tumor.〔 Some tumors grow gradually, requiring only monitoring and possibly needing no further intervention.〔 Treatments that use a person's immune system are being studied.〔 Outcome varies considerably depending on the type of tumor and how far it has spread at diagnosis.〔 Glioblastomas usually have poor outcomes while meningiomas usually have good outcomes.〔 The average five-year survival rate for brain cancer in the United States is 33%.〔(【引用サイトリンク】url=http://seer.cancer.gov/statfacts/html/brain.html )〕 Secondary or metastatic brain tumors are more common than primary brain tumors,〔 with about half of metastases coming from lung cancer.〔 Primary brain tumors occur in around 250,000 people a year globally, making up less than 2% of cancers. In children younger than 15, brain tumors are second only to acute lymphoblastic leukemia as a cause of cancer. In Australia the average economic cost of a case of brain cancer is $1.9 million, the greatest of any type of cancer. ==Signs and symptoms== Signs and symptoms of a brain tumor mainly depend on the size of the tumor and its location. The time of symptom onset depends in many cases on whether the tumor is benign or malignant, and in many cases is also related to the change in the nature of the neoplasm, from slow-growing, late-symptom-onset ''benign'' to faster-growing, early-symptom-onset ''malignant''. Symptoms of both primary and secondary brain tumors can be divided into three main categories: * Symptoms as consequences of increased intracranial pressure (often first noticed): Large tumors or tumors with extensive peritumoral swelling (edema) inevitably lead to elevated intracranial pressure which translates clinically into headaches, vomiting with or without nausea, altered state of consciousness (somnolence, coma), dilation of the pupil on the side of the lesion (anisocoria), papilledema (prominent optic disc at the funduscopic eye examination). However, even small tumors obstructing the passage of cerebrospinal fluid (CSF) can also present such symptoms. Increased intracranial pressure may result in brain herniation (i.e. displacement) of certain parts of the brain, such as the cerebellar tonsils or the temporal uncus, resulting in lethal brainstem compression. In very young children, elevated intracranial pressure may cause an increase in the diameter of the skull and bulging of the fontanelles. * Dysfunction: depending on the tumor location and the damage it may have caused to surrounding brain structures, either through compression or infiltration, focal neurologic symptoms may occur, such as cognitive and behavioral impairment including impaired judgment, memory loss, lack of recognition, spatial orientation disorders, personality or emotional changes, hemiparesis, hypoesthesia, aphasia, ataxia, visual field impairment, impaired sense of smell, impaired hearing, facial paralysis, double vision, dizziness, but more severe symptoms might occur too, such as paralysis on one side of the body hemiplegia or impairment in swallowing. These symptoms are not specific for brain tumors – they may be caused by a large variety of neurologic conditions (e.g. stroke, traumatic brain injury). What counts, however, is the location of the lesion and the functional systems (e.g. motor, sensory, visual, etc.) it affects. A bilateral temporal visual field defect (bitemporal hemianopia—due to compression of the optic chiasm), often associated with endocrine dysfunction—either hypopituitarism or hyperproduction of pituitary hormones and hyperprolactinemia is suggestive of a pituitary tumor. * Irritation: abnormal fatigue, weariness, absences and tremors, but also epileptic seizures. A benign brain tumor may be present for some years and be asymptomatic. Others might present ambiguous and intermittent symptoms like headaches and vomiting or weariness and so be mistaken for gastrointestinal disorders. In these cases secondary symptoms need to be looked into. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Brain tumor」の詳細全文を読む スポンサード リンク
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